1. Field of the Invention
The present invention relates to an apparatus for acquiring the rotational characteristics of a motor as a drive source and a control apparatus for performing control using the acquired motor characteristics.
2. Description of the Related Art
Some motor vehicles have automatic windows called “power windows”, which are so designed that when some foreign object is caught in a closing door glass (window glass), the jamming is detected quickly and the door glass is rolled back in an opening direction automatically. This is done to prevent any excessive load from bearing on the caught object. Such a door glass is driven up or down by the forward or reverse rotation of a dedicated motor, and, as such, the operation speed of the door glass changes with the rotational speed of the motor. When an object is jammed during the rising of the door glass, the operation speed thereof drops due to a reaction force of the load bearing on the object. Hence, the jamming can be detected from a drop in the rotational speed of the motor below a predetermined reference value.
The rotational speed of the motor is detected by a rotation detection sensor provided on a rotating shaft of the motor. The rotation detection sensor comprises a magnet whose north pole and south pole are oppositely disposed on the rotating shaft of the motor and hall elements that are disposed therearound. As the magnet rotates together with the rotating shaft of the motor, pulsing detection signals (hall voltages) proportional to the magnetic flux density are outputted from the hall elements. The rotational speed of the motor can be determined by calculating the rotation period of the motor from the pulse width of the detection signals. In such an arrangement, if two hall elements are disposed out of phase from each other relative to a single magnet for instance, then the rotational direction of the motor can also be detected by comparing the on and off states of the detection signals outputted from the two hall elements.
A problem with such a rotation detection sensor as described above, however, is that variation, if any, in the polarization of the north and south poles of the magnet can cause errors in the pulse width of the detection signals, which renders accurate determination of the rotational speed of the motor difficult. Moreover, provision of a plurality of hall elements can cause installation errors of the hall elements also.
To solve these problems, methods have been proposed in which a threshold value is set for detection signals outputted from the hall elements and the rotational speed of the motor is calculated from the elapsed time between the corresponding edges of the detected rectangular pulse signals (See Reference (1) in the following Related Art List, for instance)
The setting of a threshold value as described above so as to use a detection point on the edges of signals as reference enables calculation of the rotation period of the motor constantly with reference to the same point of the magnet. As a result, the effects of errors in polarization and/or installation of the hall elements can be practically eliminated. Furthermore, provision of a plurality of hall elements allows the calculation of the rotation period at every detection of the rising and falling edges of each pulse signal. And this leads to improved measuring accuracy because of shorter calculation interval of the rotational speed of the motor, for example by acquiring the rotation period at every ¼ cycle.